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1.
Langmuir ; 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-32097015

RESUMO

We report methods to synthesize sub-micron- and micron-sized patchy silica particles with fluorescently labeled hemispherical titania protrusions, as well as routes to efficiently characterize these particles and self-assemble these particles into non-close-packed structures. The synthesis methods expand upon earlier work in the literature, in which silica particles packed in a colloidal crystal were surface-patterned with a silane coupling agent. Here, hemispherical amorphous titania protrusions were successfully labeled with fluorescent dyes, allowing for imaging by confocal microscopy and super-resolution techniques. Confocal microscopy was exploited to experimentally determine the numbers of protrusions per particle over large numbers of particles for good statistical significance, and these distributions were compared to simulations predicting the number of patches as a function of core particle polydispersity and maximum separation between the particle surfaces. We self-assembled these patchy particles into open percolating gel networks by exploiting solvophobic attractions between the protrusions.

2.
Phys Rev Lett ; 123(9): 098001, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31524482

RESUMO

Switching on high activity in a relatively dense system of active Janus colloids, we observe fast clustering, followed by cluster aggregation towards full phase separation. The phase separation process is however interrupted when large enough clusters start breaking apart. Following the cluster size distribution as a function of time, we identify three successive dynamical regimes. Tracking both the particle positions and orientations, we characterize the structural ordering and alignment in the growing clusters and thereby unveil the mechanisms at play in these regimes. In particular, we identify how alignment between the neighboring particles is responsible for the interruption of the full phase separation. Our large scale quantification of the phase separation kinetics in active colloids points towards the new physics observed when both alignment and short-range repulsions are present.

3.
Soft Matter ; 12(35): 7265-72, 2016 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-27406917

RESUMO

Emulsions stabilized by solid particles, called Pickering emulsions, offer promising applications in drug delivery, cosmetics, food science and the manufacturing of porous materials. This potential stems from their high stability against coalescence and 'surfactant-free' nature. Generally, Pickering emulsions require that the solid particles are wetted by both phases and as a result, the adsorption free energy is often large with respect to the thermal energy (kBT). Here we provide the first experimental proof for an alternative scenario: non-touching (effectively non-wetting), charged, particles that are completely immersed in the oil phase through a balance of charge induced attractions and repulsions caused by van der Waals forces. These particles nonetheless stabilize the emulsion. The main advantage of this novel adsorption mechanism is that these particles can easily be detached from the interface simply by adding salt. This not only makes the finding fundamentally of interest, but also enables a triggered de-emulsification and particle recovery, which is useful in fields like enhanced oil recovery, heterogeneous catalysis, and emulsion polymerization.

4.
Langmuir ; 31(1): 65-75, 2015 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-25535669

RESUMO

We studied suspensions of sterically stabilized poly(methyl methacrylate) (PMMA) particles in the solvent cyclohexyl bromide (CHB; εr = 7.92). We performed microelectrophoresis measurements on suspensions containing a single particle species and on binary mixtures, using confocal microscopy to measure the velocity profiles of the particles. We measured the charge of so-called locked PMMA particles, for which the steric stabilizer, a comb-graft stabilizer of poly(12-hydroxystearic acid) (PHSA) grafted on a backbone of PMMA, was covalently bonded to the particle, and for unlocked particles, for which the stabilizer was adsorbed to the surface of the particle. We observed that locked particles had a significantly higher charge than unlocked particles. We found that the charge increase upon locking was due to chemical coupling of 2-(dimethylamino)ethanol to the PMMA particles, which was used as a catalyst for the locking reaction. For particles of different size we obtained the surface potential and charge from the electrophoretic mobility of the particles. For locked particles we found that the relatively high surface potential (∼ +5.1 kBT/e or +130 mV) was roughly constant for all particle diameters we investigated (1.2 µm < σ < 4.4 µm), and that the particle charge was proportional to the square of the diameter.

5.
Phys Rev Lett ; 113(24): 248302, 2014 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-25541808

RESUMO

We report spontaneous motion in a fully biocompatible system consisting of pure water droplets in an oil-surfactant medium of squalane and monoolein. Water from the droplet is solubilized by the reverse micellar solution, creating a concentration gradient of swollen reverse micelles around each droplet. The strong advection and weak diffusion conditions allow for the first experimental realization of spontaneous motion in a system of isotropic particles at sufficiently large Péclet number according to a straightforward generalization of a recently proposed mechanism [S. Michelin, E. Lauga, and D. Bartolo, Phys. Fluids 25, 061701 (2013); S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)]. Experiments with a highly concentrated solution of salt instead of water, and tetradecane instead of squalane, confirm the above mechanism. The present swimming droplets are able to carry external bodies such as large colloids, salt crystals, and even cells.

6.
J Chem Phys ; 138(11): 114903, 2013 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-23534658

RESUMO

We investigated the effect of size polydispersity on the crystal-fluid transition in hard-core repulsive Yukawa systems by means of Monte Carlo simulations for several state points in the Yukawa parameter space. Size polydispersity was introduced in the system only with respect to the hard particle cores; particles with different diameters had the same surface potential ψ0, but the charge per particle was not varied with packing fraction or distance. We observed a shift to higher packing fraction of the crystal-fluid transition of bulk crystals with a fixed log-normal size distribution upon increasing the polydispersity, which was more pronounced for weakly charged particles (ψ0 ≈ 23 mV) compared to more highly charged particles (ψ0 ≈ 46 mV), and also more pronounced for larger Debye screening length. At high polydispersities (≥0.13) parts of the more highly charged systems that were initially crystalline became amorphous. The amorphous parts had a higher polydispersity than the crystalline parts, indicating the presence of a terminal polydispersity beyond which the homogeneous crystal phase was no longer stable.

7.
J Chem Phys ; 136(5): 054904, 2012 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-22320761

RESUMO

The behaviour of two-dimensional patchy particles with five and seven regularly arranged patches is investigated by computer simulation. For higher pressures and wider patch widths, hexagonal crystals have the lowest enthalpy, whereas at lower pressures and for narrower patches, lower density crystals with five nearest neighbours that are based on the (3(2),4,3,4) tiling of squares and triangles become lower in enthalpy. Interestingly, in regions of parameter space near to that where the hexagonal crystals become stable, quasicrystalline structures with dodecagonal symmetry form on cooling from high temperature. These quasicrystals can be considered as tilings of squares and triangles and are probably stabilized by the large configurational entropy associated with all the different possible such tilings. The potential for experimentally realizing such structures using DNA multi-arm motifs is also discussed.

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